In the so-called terahertz wavelength range, 1 THz=1012 Hz; it is between infrared and microwave and includes part of millimeter wavelength (0.1 THz) to far infrared region (25 THz) as shown in FIG. 1; in other words, it is between two major zones that are based on electron and photon as the development means. In the research field of solid state physics, terahertz wavelength range is a very important spectrum because many important material characteristics energy correspond to THz wave range, for example, acceptor and donor in semiconductor, the binding energy of exciton, optical phonon, superconducting energy gap, etc. All of them fall in these wavelength section; moreover, it has very great development potential in the fields of spectral analysis, radio astronomy, telemetry, communication and biomedical science.
There are two major ways to generate terahertz radiation, namely, current surge model or photoconduction model and secondary nonlinear optical rectification model. Among them, current surge model is the generation of radiation when the optically excited carriers are accelerated by externally applied electric field, that is, it is the dipole radiation generated when photo transient is changed; however, this method is limited by the characteristic and design of the used photoconductive antenna, as well as the sensitivity of the receiver, hence, the radiation power of the terahertz electromagnetic wave system is thus restricted; in secondary nonlinear optical rectification model, the incident ultra-short optical pulse is coupled with the nonlinear polarization coefficient of the crystal so as to synthesize terahertz electromagnetic wave; however, a polarizer is needed in this method.
FIG. 2 illustrates the prior art metal wire grid polarizer structure. The prior art polarizer is mainly metal line grating polarizer 20, with its principle based on the light reflection and the transmission; that is, array is made on the transparent substrate 21, and this array is formed by closely spaced the parallel metal lines 22; therefore, the preparation of metal line grating polarizer will need to use micro-processing techniques such as metal deposition and etching that involves multi-layer metals; however, metal line grating polarizer prepared in this way not only has the disadvantage of high cost, but also the metal line can easily get damaged.